Electronic apparatus typically includes therein electronic modules such as different subsystems, electronic circuits, and so on. These modules usually require different supply voltages for achieving normal operations thereof. For example, an analog power amplifier may require a supply voltage of 3.5 volts, a digital processing module may require different supply voltages of 1.8 volts, 5 volts etc. To ensure normal operations of the respective electronic modules in the electronic apparatus, a voltage converter is required to convert a DC voltage (e.g., a voltage from a battery) into another different DC voltage as required by an individual module, that is, a specific input voltage Vin is converted into a different output voltage Vout.
In existing voltage converters, for example, electric energy at an input is stored transitorily in an inductor and/or a capacitor (i.e., a charging process is performed), and thereafter electric energy is released at a different voltage at an output (i.e., a discharging process is performed), so that the input voltage Vin is converted into the desired output voltage Vout. Accordingly, a drive signal is employed to drive a control device (e.g., a switch) in the voltage converter, by which the charging process and the discharging process are controlled so as to obtain the desired output voltage Vout, that is, a turn-on time Ton during which a corresponding switch is closed to charge and a turn-off time Toff during which the switch is open to discharge are controlled. The turn-on time Ton corresponds to a pulse width of the drive signal.
In the operation process of the voltage converter, a situation where impedance of a load (e.g., an electronic module) driven by its output voltage Vout changes may occur, for example, when an operation state of the electronic module changes, and its impedance value relative to the voltage converter will change. In this case, in order to improve conversion efficiency of the voltage converter, it may need to adopt different control methods to control the charging operation and discharging operation of the voltage converter. For example, when the load driven by the output voltage Vout is a medium or heavy load whose load value is relatively large, a continuous control mode (CCM) may be adopted to control the voltage converter; when the load driven by the output voltage Vout is a light load whose load value is relatively small, a discontinuous control mode (DCM) may be adopted to control the voltage converter. In the continuous control mode, the drive signal drives a control device in the voltage converter to make the voltage converter perform charging and discharging operations continuously; and in the discontinuous control mode, the drive signal drives a control device in the voltage converter, so that the voltage converter can halt for some time after performing charging and discharging operations, and thereafter again perform charging and discharging operations.
When the load driven by the output voltage Vout changes from a medium load into a light load, the control mode of the voltage converter needs to be switched from a continuous control mode to a discontinuous control mode. Typically, mode switching is carried out based on load current on the driven load, and threshold of the load current for carrying out mode switching usually varies along with the input voltage Vin and the output voltage Vout of the voltage converter, which makes it difficult to perform mode switching accurately, thus lowers power efficiency of the voltage converter accordingly. Further, variation of the on-off frequency of the control device will also increase noise in the output voltage Vout.